The present invention relates to surgical angioplasty balloon procedures and more particularly relates to stent compression method for particular use in pre-surgical securement of an angioplasty stent onto a balloon catheter for subsequent implantation of the stent in an angioplasty procedure.
A common method of treatment used in restoring blood flow through a diseased segment of a blood vessel is balloon angioplasty. The therapy generally involves the use of a balloon catheter. The balloon catheter is introduced into the cardiovascular system of a patient through the brachial or femoral artery and advanced through the vasculature until the balloon attached to the distal end of the catheter reaches the diseased vessel. The balloon is placed across the diseased vessel segment and is inflated with sufficient pressure to cause the deposit on the intravascular surface to compress against the vessel wall. The balloon is then deflated to a small profile, so that the balloon catheter may be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
Angioplasty of an artery to correct flow obstruction in the vessel may stimulate excess tissue proliferation which then blocks (restenosis) the newly reopened vessel. The physician would usually need perform a second angioplasty procedure. Alternatively, a more drastic procedure, such as a surgical bypass operation may be required to repair or strength the vessel. To reduce the likelihood of restenosis and to strengthen the diseased vessel segment, an intravascular stent may be implanted within the segment of the diseased vessel to maintain vascular patency. The stent is typically transported through the patient""s vasculature where it has a small delivery diameter, and then is expanded to a larger diameter, often by the balloon portion of the catheter.
Stents are tubular structures, which are radially expandable to hold a narrowed blood vessel in an open configuration. While stents are most often used to xe2x80x9cprop openxe2x80x9d blood vessels, they can also be used to reinforce collapsed or narrowed tubular structures in the respiratory system, the reproductive system, biliary ducts or any other tubular body structure.
Since the catheter and stent will be traveling through the patient""s vasculature, and in many cases through the coronary arteries, the stent must have a small, delivery diameter and must be attached to the catheter until the physician is ready to implant it. Thus, the stent must be positioned on the balloon catheter such that it does not interfere with delivery, and it must not slip off of the catheter before it reaches the desired location for deployment.
In conventional procedures where the stent is placed over the balloon portion of the catheter, it is necessary to crimp the stent onto the balloon portion to reduce its diameter and to prevent it from sliding off the catheter when the catheter is advanced through a patient""s vasculature. Non-uniform crimping can result in sharp edges being formed along the uneven surface of the compressed stent. In addition, non-uniform stent compression may result in a stent/catheter profile that is larger than necessary. Where the stent is not reliably compressed onto the catheter, the stent may slide off the catheter and into the patient""s vasculature prematurely as a loose foreign object, which may cause thrombosis. Thus, it is important to ensure the proper compression of a stent onto a catheter in a uniform and reliable manner.
Manual crimping of the stent by hand tends to result in uneven compression due to uneven application of force. Furthermore, it is difficult to determine when a uniform and reliable compression has been achieved. In addition, due to the flexible nature of the stent, some self-expanding stents are difficult to load by hand onto a balloon catheter. Minimizing direct human manipulation may decrease the likelihood of human error, and increase the consistency of the compression procedure. Hence, there is a need for a device for reliably compressing a stent onto a catheter.
There have been mechanisms devised for loading a stent onto a catheter. Examples of such compression devices are disclosed in U.S. Pat. No. 5,911,452, issued Jun. 15, 1999 to Yan, which shows a chamber with flexible tubular diaphragm into which a deflated balloon catheter can be inserted with the stent and the chamber is pressurized to crimp the stent onto the deflated catheter balloon; U.S. Pat. No. 6,009,614, issued Jan. 4, 2000 to Morales, which shows another stent crimping chamber utilizing fluid pressure to crimp the stent onto a deflated catheter balloon; U.S. Pat. No. 5,810,838, issued Sep. 22, 1998 to Soar, which shows further examples of pressurized chambers and collapsible tubular sleeves for compressing stents onto balloon catheters; U.S. Pat. No. 5,971,992, issued Oct. 26, 1999 to Solar, which shows yet another examples of pressurized chamber; U.S. Pat. No. 5,746,764, issued May 5, 1998 to Green et al., which shows further devices for compressing stent onto balloon catheters that include both vacuum and pressurizing fluid pressure means for compression of the stent onto the catheter balloon; U.S. Pat. No. 5,944,735, issued Aug. 31, 1999 to Green et al., which show yet another example of the stent compression device; U.S. Pat. No. 5,972,028 issued Oct. 26, 1999 to Rabenau et al., which shows another variaton of the Green et al. devices supra; U.S. Pat. No. 5,860,966, issued Jan. 19, 1999 to Tower, which shows another version of a stent compression apparatus employing a pressurized diaphragm go compress the stent; each of which is incorporated herein by references in its entirety.
However, the above-cited references do not teach nor suggest inflating the angioplasty balloon prior to compressing of the stent over the balloon. Neither does the above cited references suggest any other means to maintain an internal pressure within the stent to provide a more controlled compression process.
Although the above-described methods by which stents are crimped may be more reliable and constant than manual compression of the stents, these approaches does not overcome problems due to uneven structural collapsing rate of the stent. Stents are mechanical devices that are designed to counter compression pressure when they are expended. However, due to the mechanical nature of the stent, their internal structure is generally not completely homogeneous. The structure of the stent itself could lead to redistribution of pressure within the stent leading to uneven collapse of the stent.
A method that enhances uniform distribution of the compression pressure and at the same time controls the rate contraction of the stent during the compression process may allow even distribution of pressure during the stent compression process and thus, achieve superior placement of the stent over the angioplasty balloon.
One aspect of the present invention provides for uniform compression of an agioplasty stent over a catheter. In another aspect of the invention, a delivery balloon is inflated inside a stent prior to compressing and securing the stent over the delivery balloon. In yet another aspect of the invention, the stent compression rate, and/or the pressure inside the balloon and the chamber, are carefully controlled during the stent compression process.
One variation of the invention is a method for securing a stent over a balloon on a catheter which comprises the following steps: providing an uncompressed stent; inserting an angioplasty balloon in a deflated state into the stent until the stent is centered upon the balloon; inflating the balloon until the balloon is about the size of the inner diameter of the stent; placing the stent/balloon unit into a compression chamber; applying a positive compression pressure to the outer circumferential surface of the stent; increasing the compression pressure while at the same time decreasing the pressure within the balloon.
In another variation, the deflated balloon with a stent placed around it may be inserted into the compression chamber before the balloon is inflated. The balloon is inflated inside the chamber, followed by the compression process. In yet another variation, the stent may be inserted into the chamber first. After the stent is secured within the chamber, the balloon is inserted within the stent and may then be centered before it is inflated.
In another aspect of the invention, the pressures for compressing the stent and inflating the balloon may be monitored and adjusted with separates valves and/or pressure pumps. In another variation, one or more feed back control mechanisms may be adapted to control the stent compression process. Pressure sensors may be adapted for monitoring the pressure inside the pressure chamber and/or the pressure inside the balloon. In yet another variation, a computer is used for automated control of the stent compression process.
Various pressure sources that are well known to one skilled in the art may be used to provide the pressure for stent compression and for maintaining the balloon in an inflated state. The pressure source includes, but is not limited to, pneumatic pressure and hydraulic pressure.
The balloon and the inflation chamber may be inflated with the same pressure source or alternatively with independent pressure sources. Various pressure pumps that are well known to one skilled in the art may be adapted for providing the inflation pressure needed in the stent compression process.
In one variation, the compression is achieved with hydraulic pressure. Fluids (e.g. water, oil, saline) may be used to inflate a membrane or elastic surface, such that when the membrane or the elastic surface is inflated, it expends inward in a circumferential manner and compresses the object inside the chamber. In another variation, the compression is achieved with pneumatic pressure. Air or gas (e.g. nitrogen, helium, argon, carbon dioxide, or a mixture thereof) may be used to inflate a membrane or elastic surface for compressing the stent. The balloon may also be inflated with fluid (e.g. water, saline), air or gas (e.g., nitrogen, helium, argon, carbon dioxide or a mixture thereof).
With the inner circumferential surface of the stent supported during the compression process, the collapse of the stent will be more controlled and problems associated with non-uniform crimping, such as nicks and kinks along the compressed stent, or sharp edges being formed along the uneven surface of the crimped stent, may be minimized. Furthermore, uniform compression achieved through this process may also minimize dead space between the stent and the angioplasty balloon and a minimal profile for the stent and catheter assembly may thus be achieved.
These and other embodiments, features and advantages of the present invention will become more apparent to those skilled in the art when taken with reference to the following more detailed description of the invention in conjunction with the accompanying drawings.